Regenerator



Sept. 5, 1967 J, VAN GEU ET AL 3,339,627

REGENERAT OR Filed March 22, 1965 INVENTORS. JOHANNES R. VAN GEL NS JANMULDER AGENT United States Patent corporation of Delaware Filed Mar. 22,1965, Ser. No. 444,099

5 Claims. (Cl. 165-4) The invention relates to a regenerator comprisinga filling mass consisting of a plurality of stacked metal gauzes.

This kind of regenerators is known and is employed for example incoldgas refrigerators and other 'devices for producing cold. Theregenerator is traversed altenately in one direction by a compressedmedium, which gives off heat to the filling mass and in the otherdirection by an expanded medium which absorbs heat from the fillingmass.

A problem involved in this kind of regenerators resides in that thematerial of the gauze, for example copper, Phosphor bronze etc. does nothave an adequately high specific heat at very low temperatures. Thismeans that at these low temperatures the filling mass cannot store anadequate quantity of heat, neither can it give off an adequate quantityof heat. When these known regenerators are employed, it is therefore notpossible to attain extremely low temperatures.

It is known that other materials still have a satisfactory specific heatat said low temperatures, but these materials have the disadvantage thatthey are all so weak and have such a small tensile strength that nogauze can be made from them.

The use of gauzes as a filling mass has the advantage that owing totheir structure such gauzes have point contacts only locally. This meansthat the thermal resistance between two adjacent gauzes is fairly highwithout the need for using additional insulating means. Therefore, thethermal conductivity in the direction in which the medium passes throughthe filling mass will be small. A further advantage of gauzeregenerators is that the medium is not compelled to follow fixedchannels of flow so that behind each gauze the medium can mix to someextent in a transverse direction.

The invention has for its object to provide a regenerator which operatessatisfactorily at extremely low temperatures, while the favourableproperties of the gauze are maintained.

The regenerator according to the invention is characterized in that thewires of the metal gauze are provided after the manufacture of the gauzeat their surface with a metal layer of a metal which has a comparativelyhigh specific heat below 100 K.

In a further advantageous embodiment of the regenerator according to theinvention the metal gauze is made of wire material having a diameter ofnot more than 100 microns while the meshes of the gauze have a width atleast equal to the wire diameter, the metal gauze being provided with ametal layer having a thickness smaller than half the size of mesh,preferably smaller than 90% of half the size of mesh. Thus a regeneratoris obtained which has a very satisfactory degree of efficiency at verylow temperatures, While the thermal conductivity in the direction offlow is small without additional precautions. The specific dimensions ofthe gauzes have been chosen for a good filling factor; a good heattransfer surface, and a sufficient mass of material for storing heat.

It has been found by surprise that the metal layers according to theinvention can be electrolytically deposited on the gauze. The gauzestructure (hills and valleys) is maintained very satisfactorily, whilstthe meshes are not closed. Of course, it is also possible to apply themetal layer to the gauze by chemical agency or by vapour-deposition.

' In 'a further embodiment the applied metal layer may consist of ametal of the group comprising lead, mercury, cadmium, thallium, rareearth metals, caseium, indium, bismuth or alloys thereof.

There is a possibility that at the contact areas of adjacent gauzes thesoft surface layer should be flattened or even be pressed away, so thatthe thermal conductivity in the direction of flow might increase.

In order to overcome said risk an advantageous embodiment of theregenerator according to the invention has the feature that the surfacelayer consisting of a metal having a comparatively high specific heat atvery low temperatures below K. is coated with a further layer consistingof a metal having a greater hardness than the first-mentioned layer.

The gauzes engage each other in this case with their hard surfaces, sothat the contact surface and hence the thermal conductivity are smaller.

In a further advantageous embodiment the metal of the further surfacelayer is not only harder but also has, below 100 K., a smaller thermalconductivity than the material of the first surface layer.

The thickness of the further surface layer in a further advantageousembodiment is at the most 10 microns.

The material of the further surface layer my be chromium, nickel, ironor alloys hereof.

In a further advantageous embodiment of the regenerator according to theinvention the wires of the gauze are provided with a number of surfacelayers, which consist alternately of a metal having a comparatively highspecific heat below 100 K. and a metal having a greater hardness and acomparatively low thermal conductivity.

In the manner described above a very simple regenerator can bemanufactured at low cost, which operates still satisfactorily at verylow temperatures.

FIG. 1 is a cross-sectional view of the regenerator housing 1 having astack 2 of Wire gauzes 3 therein.

FIG. 2 is a cross-sectional view of the wire gauges 3 having a nucleus 4for example of copper or phosphorus bronze and an outer layer 5 of amaterial having a high heat capacity at low temperature, for example,lead.

FIG. 3 is a cross-sectional view of the wire gauze 3 in which a copperor phosphorus bronze nucleus 6 is provided with a layer 7 of a materialhaving a high heat capacity at low temperatures, such as lead and anouter layer 8 is supplied provided with a metal having a greaterhardness than the layer 7, such as chromium.

It should be noted that from British patent specification 931,260 thereis known a regenerator, the filling mass of which consists of a numberof stacked perforated metal plates provided With a surface layer of ametal having a satisfactory thermal capacity at a low temperture. Adisadvantage of this regenerator is that additional expedients (spacers)are required for restricting the thermal conductivity in the directionof flow. The regenerator is therefore expensive. The invention obviatesthis disadvantage completely since gauzes, owing to the maintenance oftheir natural gauze structure, have only point contacts with each other,so that a satisfactory thermal resistance in the direction of flow isobtained.

What is claimed is:

1. A regenerator comprising a housing, a filling mass constituted of aplurality of stacked metal gauzes, said meal gauzes being provided witha coating constituted of a first metal layer having a comparatively highspecific heat below 100 K. and a second layer of a metal having agreater hardness than said first layer.

2. A regenerator as claimed in claim 1 wherein the r 3 material of saidsecond layer has a comparatively low thermal conductivity below 100 K.

3. A regenerator as claimed in claim 1 wherein said second layer has athickness of not more than 10 microns.

4. A regenerator as claimed in claim 1 wherein said second layer isselected from the group consisting of chromium, nickel, iron and alloysthereof.

5. A regenerator as claimed in claim 2 wherein said coating isconstructed alternately of said metal having a comparatively highspecific heat below 100 K. and said metal having a greater hardness anda comparatively low thermal conductivity below 100 K.

4 References Cited UNITED STATES PATENTS 3,216,484 11/1965 Gifiord 1654FOREIGN PATENTS 157,334 6/ 1954 Australia. 609,232 1 1 1960 Canada.

65,498 4/ 1950 Netherlands.

10 ROBERT A. OLEARY, Primary Examiner.

A. W. DAVIS, Assistant Examiner.

1. A REGENERATOR COMPRISING A HOUSING, AFILLING MASS CONSTITUTED OF APLURALITY OF STACKED METAL GAUZES, SAID MEAL GAUZES BEING PROVIDED WITHA COATING CONSTITUTED OF A FIRST METAL LAYER HAVING A COMPARATIVELY HIGHSPECIFIC HEAT BELOW 100*K. AND A SECOND LAYER OF A METAL HAVING AGREATER HARDNESS THAN SAID FIRST LAYER.